The proposed work centers on the high molecular weight high mobility group (HMG) nonhistone chromatin proteins. We have previously shown that HMG-1 and HMG-2 occur in cultured hepatoma cells in much higher amounts than in adult rat liver and that both proteins possess preferential affinity for single-stranded DNA. Using a large scale phosphocellulose isolation procedure, we will purify HMG-1 and HMG-2 from chicken erythrocytes. Antibodies will be obtained in rabbits against each protein, and radioimmunoassays will be developed. We will also study the strength of binding of the purified proteins to single-stranded and double-stranded DNA at various solvent conditions. In addition we will study the effect of the proteins on the digestion of DNA by several nucleases commonly used in the study of chromatin structure.